Communications systems frequently include a plurality of network nodes, which are coupled to access nodes through which end nodes, e.g., mobile devices, are coupled to the network. The access nodes may be, for example, sectorized base stations, supporting a physical attachment point in each sector. Typically, each physical attachment point corresponds to a set of layers including a physical layer, a media access control (MAC) layer, and a logical link control (LLC) layer.
In certain communication systems, an end node can simultaneously have physical connections to a plurality of physical attachment points. In such cases, a plurality of sets of physical, MAC and LLC layers is typically implemented in the end node, a different one of said plurality of sets for each physical attachment point the end node is connected to. Among other things, the LLC layer is responsible for segmentation of packets of upper layers into segments that can be transported by the MAC layer, which we will call MAC frames. The MAC layer generally does not guarantee delivery, i.e., it is possible that a transmitted MAC segment is not decoded properly by the receiver. The LLC layer may implement an automatic repeat request (ARQ) protocol which re-transmits those MAC frames whose transmission has failed.
Consider an end node simultaneously having physical connections to a plurality of physical attachment points, each having independent LLC layers implementing an ARQ protocol. In this case, each upper layer packet has to be transmitted in full over one of said plurality of physical attachment points. That is each of the MAC frames an upper layer packet is segmented into by the LLC layer has to be transmitted over the same physical connection so that it is successfully re-assembled by the receiver LLC layer coupled to said physical attachment point. This poses a constraint on the access node and end node implementations that could adversely affect performance. For example in a wireless communications system the channel conditions of physical connections may vary rapidly, the condition of a physical connection could deteriorate while some of the MAC frames of an upper layer packet have already been sent over this physical connection. In such a case the transmitter could choose to keep trying to send the remaining MAC frames of said upper layer packet over the deteriorated physical connection, or to give up and restart the transmission of the upper layer packet over another physical connection.
In addition, it would also be desirable if methods and apparatus were developed which allowed for a plurality of physical points of attachment being coupled to a single LLC layer. It would be beneficial if a logical link between an end node and an access node could be supported by a plurality of physical connections. It would also be advantageous if each of the different MAC frames an upper layer packet is segmented into could be transmitted over any of the physical connections supporting a logical link.
In view of the above discussion, it should be appreciated that there is a need for methods and apparatus to implement access nodes and end nodes that allow for a plurality of simultaneous physical connections supporting a single logical link.